The present invention relates to a weighing apparatus and to a method of making such an apparatus. More specifically, the invention relates to platform scales of the electronic type.
Prior art electronic scales are equipped with strain gage transducers which are separately manufactured and then secured to a platform in many different arrangements. Typically, a platform structure is supported in each corner by a single transducer arranged between the platform proper and a base. In another prior art scale the platform structure is secured to the base by flexural members and the load on the platform proper is sensed by a single transducer connected between the upper platform and the base structure. In still another version a single transducer supports an upper platform on a base and the flexural members form an integral part of the single transducer.
Where four separate transducers are required to support the platform on a base, one transducer is normally mounted in each corner. This type of structure is rather expensive since four separate transducers must be fabricated and it is expensive to provide each transducer with the precision compensation and calibration characteristics which are necessary for precision weighing. Once the individual transducers, the upper platform and the base have been assembled, in itself an expensive operation, the entire assembly must again be calibrated and adjusted to minimize effects of eccentric load applications. The additional electronic components required for the reduction of eccentric load effects also contribute to increased expense.
While in the prior art, wherein the platform is connected to the base by flexural members, the number of transducers is reduced, the flexural members and the base must be carefully assembled and adjusted so that the single transducer will sense only the vertical load applied to the upper platform. Making such scales insensitive to off-center loads has been found to be difficult, time consuming, and expensive. Substantially the same considerations apply to a further prior art structure wherein the flexural members are an integral part of the single transducer. This type of structure is also sensitive to off-center loads unless expensive mechanical or electronic adjustments are made to reduce the effects of off-center loading.
In many of the prior art structures overload protection is not provided or if it is, the expense of doing so is considerable.